This type of hydroxylamine preparation process (see, e.g., U.S. Pat. No. 3,767,758 and the British Pat. Specification No. 772,693) is today used on a large scale. The hydroxylamine thus produced finds extensive use as starting material for the oximation of cyclohexanone into cyclohexanone oxime, which is in turn rearranged to form caprolactam.
In the production of hydroxylamine it has, however, been observed that when the hydroxylamine, in aqueous solution, is in contact with the catalyst containing platinum and/or palladium, and in the absence of hydrogen, it can decompose, with the formation of N.sub.2 O.
Under the usual process conditions used for the production of hydroxylamine, hydrogen is normally present in the liquid phase in the form of widely-dispersed small gas bubbles. Under those circumstances the said decomposition of hydroxylamine to N.sub.2 O is normally not induced. However, in practice the hydroxylamine salt solution may in fact come in contact with the catalyst in the absence of hydrogen under certain circumstances. This is particularly true when the production process is for some reason temporarily interrupted or otherwise upset (e.g., for external reasons or equipment failure). In such an event, there is then the risk that (a) said decomposition will be induced and (b) the resulting N.sub.2 O will form, with the hydrogen present outside the liquid phase, an explosive N.sub.2 O/H.sub.2 mixture. Hydrocarbons, which may also be present in the hydrogen gas feedstreams, may also form an explosive mixture with the N.sub.2 O. (See e.g. Bulletin 503, 1952 and 627, 1965 Bur. of Mines). A substantial hazard is thus present under certain process upset conditions which may unavoidably occur during operation of the process, and which it has obviously been desirable to avoid.